Wednesday, January 2, 2008

Voltage variations and power cuts adversely affect various equip- ment such as TVs, VCRs, music systems and refrigerators. This simple circuit will protect the costly equipment from high as well as low voltages and the voltage surges (when power resumes). It also gives a melodious tune when mains power resumes. When mains voltage is normal, the DC voltage at the cathode of zener diode D4 is less then 5.6V. As a result transistor T1 is in ‘off’ state. The DC voltage at the cathode of zener diode D5 is greater than 5.6V and as a result transistor T2 is in ‘on’ state. Consequently, relay RL1 gets energised, which is indicated by lighting up of green LED. Under high mains voltage condition, transistor T1 switches to ‘on’ state because the voltage at cathode of zener diode D4 becomes greater than 5.6V. Consequently, transistor T2 switches to ‘off’ state, making the relay to de-energise Under low mains voltage condition, transistor T1 switches to ‘off’ state and as a result transistor T2 also switches to ‘off’ state, making the relay to de-energise.

Timer IC 555 in the circuit is configured to operate in a monostable mode. The pulse width is about 10 seconds with the timing component values used in the circuit. When the power resumes after a break, pin 2 of IC 555 goes low briefly and this triggers it. Its output makes music IC UM66 to operate through transistor T3. Simultaneously, transistor T1 also gets forward biased as the monostable IC1 output is connected to its base via diode D8 and resistor R7. As a result, transistor T1 conducts and biases transistor T2 to cut off. Thus relay RL1 remains de-energised for the duration of mono pulse and the load is protected against the voltage surges.

To adjust presets VR1 and VR2, you may use a manually variable auto-transformer. Set the output of auto-transformer to 270V AC and connect it to the primary of transformer X1. Adjust preset VR1 such that relay RL1 just de-energises. Next set the output of auto-transformer to 170V AC. Now adjust preset VR2 such that relay RL1 again de-energises. Volume control VR3 may be adjusted for the desired output volume of the tune generated by IC UM66.

General Discussion

User Agreement

The creator of THIS PAGE or the ISP(s) hosting any content on this site take NO responsibility for the way you use the information provided on this site. These circuits here are for educational purposes only and SHOULD BE VIEWED ONLY. If you download any files to view them, you are agreeing to delete them within a 24 hour period. If you are affiliated with any government, or ANTI-Piracy group or any other related group or were formally a worker of one you CANNOT enter this web site, cannot access any of its files and you cannot view any of the HTML files. All the objects on this site are PRIVATE property and are meant for previewing only. If you enter this site without following these agreements you are not agreeing to these terms and you are violating code 431.322.12 of the Internet Privacy Act signed by Bill Clinton in 1995 and that means that you CANNOT threaten our ISP(s) or any person(s) or company storing these files, cannot prosecute any person(s) affiliated with this page which includes family, friends or individuals who run or enter this web site. IF YOU DO NOT AGREE TO THESE TERMS THEN LEAVE.

Disclaimer

All files are found using legitimate search engine techniques. This site does not and will not condone hacking into sites to create the links it list. We will and do assume that all links found on the search engines we use are obtained in a legal manner and the webmasters are aware of the links listed on the search engines. If you find a URL that belongs to you, and you did not realize that it was "open to the public", please use the report button to notify the blogmaster of your request to remove it. This is not an invitation for webblog haters to spam with requests to remove content they feel that is objectionable and or unacceptable. Proof of URL ownership is required.

NOTICE: This Blog Has Already Been Reviewed And Accepted By Blogger.com